The present invention relates to scanning or pattern recognition devices. It is particularly suited to portable hand-held scanning or pattern recognition devices employing light emitted from a coherent light source, such as a laser, in the reading of bar code symbols.
In the last number of years bar code symbols have achieved increased acceptance as a recognition indicia commerical products. This development has been especially significant in identifying various packaged food, which serves to facilitate handling at both the wholesale and retail level. For example, various bar codes readers and laser scanning systems have been developed to decode the bar code symbol pattern into a multiple digit representation which speeds-up the often lengthy supermarket check-out process while, simultaneously, providing an accurate and efficient means for inventory control. These devices are generally fixedly mounted, with the items to be scanned generally moved into position a known distance from the reading beam.
More recently, portable hand-held scanning devices have been developed. A major disadvantage of these hand-held scanning devices for reading bar codes is the rather distinct and severe limitations insofar as scanning distance is concerned, specifically the distance between the bar code and the scanning device within which meaningful pattern recognition can be achieved. The user must aim the beam, which is generally invisible to the human eye, to insure that the object to be scanned is within the acceptable depth of field for proper reading, i.e., the distance over which the image being scanned is sufficiently in focus to be read.